Smith cub battery ground
- Thread starter Phil Sc
- Start date
pittsdriver
MEMBER
irishfield
Registered User
Penetanguishene, Ontario Canada
Please put some rubber nipples over those + terminals !
skywagon8a
MEMBER
SE Mass MA6
This is where I put mine. 
This picture is just the temporary battery. I used a Odyssey PC-925 for the permanent battery. The ground strap is bolted to the extended baggage floor frame (which is welded in several places to the tubing for adequate low resistance current flow). Backcountry was supposed to weld on a ground tab but did not. The battery is located as far aft as possible (without major alterations) for weight and balance purposes. I wanted it further aft but, it would have been too cramped between the control cables.
This picture is just the temporary battery. I used a Odyssey PC-925 for the permanent battery. The ground strap is bolted to the extended baggage floor frame (which is welded in several places to the tubing for adequate low resistance current flow). Backcountry was supposed to weld on a ground tab but did not. The battery is located as far aft as possible (without major alterations) for weight and balance purposes. I wanted it further aft but, it would have been too cramped between the control cables.Attachments
Last edited:
pittsdriver
MEMBER
There are nipples on all my terminals. That picture was taken before the airplane was finished. Don
Dave Prizio
Registered User
Tustin, CA
The best way to ground your battery is to run a big fat wire up to a ground bus where you should ground everything in the plane. Do not use the airframe as a ground conductor. For more on this read Bob Nuckolls' Aeroelectric Connection, which you can find athttp://www.aeroelectric.com/. Regrettably this adds weight, but it solves other problems and makes it less likely that your cage will become magnetized.
skywagon8a
MEMBER
SE Mass MA6
Dave Prizio,
Running a ground conductor may be the best way to complete the circuit. Other than in a composite construction, one would be hard pressed to find a large manufacturer who does not use the airframe as the ground portion of the circuit.
Running a ground conductor may be the best way to complete the circuit. Other than in a composite construction, one would be hard pressed to find a large manufacturer who does not use the airframe as the ground portion of the circuit.
mike mcs repair
Registered User
chugiak AK
Thats kinda defeats the purpose, as you have all the noisy grounds also included on ground buss again...
I like to just run a seprerate ground for radio & intercom from battery.. A 16 or 14 ga is fine...
skywagon8a
MEMBER
SE Mass MA6
This from: http://www.aeroelectric.com/articles/Battery_Grounds/Battery_Grounds.html "Having said that, a time proven compromise that does not materially affect noise issues is to use the airframe as ground for the following items:
- Battery
- Strobe supply
- Landing, nav and taxi lights
- Pitot heat
- Hydraulic pumps for gear"
Only as long as the minus of the battery wasn't grounded to the frame otherwise your "separate ground for radio" creates a ground loop. Battery negative-->radio chassis--->fuselage tubing--->battery negative, or maybe battery negative-->radio chassis-->antenna shield--> wing to fuselage connection-->fuselage to battery. With grounds you really want it only one way to avoid noise. Remember with noise your dealing with AC (I'm including DC switching events in AC), not DC and it's "impedance", not "resistance" (DC) that is the problem with the various routes.
Last edited:
You know thinking on this, the aircraft electrical system really sucks from a noise/engineering standpoint. With the chassis of everything grounded any separate ground wires are potential ground loops and you can't run heavy ground wires to each device and insulate them or even an area from each other. EMP grounds should be wide thin pieces of copper strap since the pulse only travels on the surface anyway. Stranded wire is verboten for proper (noise) grounding. The list goes on and on.
Last edited:
Steve Pierce
BENEFACTOR
Graham, TX
A factory Super Cub has a ground lug welded to the "V" where the flap cable splits from a single cable to "Y" out to each wing. Short ground cable from the battery.
mike mcs repair
Registered User
chugiak AK
nah...
that would imply my ground path to battery terminal was intermittent, but since its as great as great can get, it's the best path.... No current can/will flow through any of the others....
http://en.wikipedia.org/wiki/Ground_loop_(electricity)
Mike I respectfully "disagree". Maybe I misunderstood and you are providing the ONLY path to ground with your wire and then I back down from what I write below. Second I am talking "noise", not DC so we are probably talking apples to oranges. DC doesn't care about ground loops. It will just split according to ohms law for multiple resistances in parallel. By the way it doesn't do: "No current can/will flow through any of the others" but will have some proportional split. Maybe 99.99% on one conductor and .01% on the other but it will split. A ground loop can exist anywhere you have two or more paths (even with internal coupling say through a bypass capacitor inside a radio between chassis and case) to ground. Remember with noise were talking either continuous AC (radio frequency or maybe digital information) or even a single "event" such as a switch opening and closing. Impedance "happens" when an AC signal is placed across a conductor. IT is measured in ohms because it acts exactly like regular resistance with a few kinky differences. It happens because when voltage is applied to a conductor the FIRST thing that happens, before max current flows through it is that a magnetic field builds up around the conductor. I know you know about this from a past reference you made to the "left hand" rule. With DC this happens for a brief part of a second when a switch is closed. At first (briefly) no current flows as if the conductor were an insulator while the field builds to a quiescent state and then the current builds steadily from there on based on ohms law for DC (note that ohms law for DC doesn't ever actually work for a brief period of time anywhere). With AC and depending on the frequency, the magnetic field may never get built up completely before it changes direction so you can have a situation where (radio relies on this effect) current NEVER flows or is "impeded". Back to our two grounds: Chances are good one of them will have different magnetic properties than the other and that's the rub. One will more than likely "impede" or present a different "AC resistance" than the other. Now you have a different potential or voltage between the conductors. Your perfect grounds are not so perfect anymore. With different lengths this will cause an "out of phase" condition and wonderful new problems can arise like broadband noise and arcing and so on as the two (really now very different) out of phase signals mix in so many wonderful new and often unpredictable ways (at least for mortals). I dealt with these things on mountain top sites and 911 centers for years. Probably the main reason I have no hair left.
I found this article and briefly read it and maybe it will be interesting to try and understand what I was trying to say above (I am no teacher):
http://www.eetimes.com/ContentEETimes/Documents/Duff_Ch_5.pdf
I'm not just splitting hairs on this. Noise was mentioned in some of the posts above and many threads have been written about owners having weird radio noise or intermittent control problems and much of the time these can be traced back to a few random volts triggering some device or other, with the noise coming in on the power cable. I am just saying two grounds to the same device can sure set that up.
If you want to avoid weird situations in the aircraft that make the radio guy look dumb to the owner and the owner frustrated try to avoid ground loops.
Mi. ( Yooper)
Help !!
So, we have seen a few pros and cons to two different scenarios of grounding in this thread....I am in the process of wiring my Smith Cub as well, and now I am really confused, I like the idea of grounding to the air frame via a short ground wire from the battery to the air frame, saves some weight and Money not having to buy any more heavy copper wire for a second run up behind the panel, and by the way I have the under seat battery mount, so here are my questions, if you ground to the air frame then how do you ground the rest of your electrical system? do you mount a bus bar directly to the air frame behind the panel for your ground terminations? what about noise? would running a separate ground using light wire (14 gage) back to the battery (like mike suggested) be the solution to the noise problem for the radio and intercom? or would this set us up for ground looping and noise issues as QSMX 440 implies, also ( this might be a dumb question) does grounding to the frame induce electrolysis which in turn starts the corrosion process with all the dissimilar metals and fasteners?? I really have to do some more research before I proceed, any more input greatly appreciated,Thanks in advance.
Rick
So, we have seen a few pros and cons to two different scenarios of grounding in this thread....I am in the process of wiring my Smith Cub as well, and now I am really confused, I like the idea of grounding to the air frame via a short ground wire from the battery to the air frame, saves some weight and Money not having to buy any more heavy copper wire for a second run up behind the panel, and by the way I have the under seat battery mount, so here are my questions, if you ground to the air frame then how do you ground the rest of your electrical system? do you mount a bus bar directly to the air frame behind the panel for your ground terminations? what about noise? would running a separate ground using light wire (14 gage) back to the battery (like mike suggested) be the solution to the noise problem for the radio and intercom? or would this set us up for ground looping and noise issues as QSMX 440 implies, also ( this might be a dumb question) does grounding to the frame induce electrolysis which in turn starts the corrosion process with all the dissimilar metals and fasteners?? I really have to do some more research before I proceed, any more input greatly appreciated,Thanks in advance.
Rick
Last edited:
Well I'll give you some things to think about. What follows is a discussion about noise and interference NOT ABOUT DC. In the real world there are other considerations that will force a compromises. For instance the following does NOT take into account FAA requirements, Aviation standard practices, individual equipment needs, liability, vibration in the mobile environment, etc. Read at your own risk. It's just my opinion about a "ground" discussion.
Another thing to realize is that both AC and DC can exist on the same conductor at the same time. It would be very possible to power a wing tip light from the battery over the coax going to the radio antenna. It's important to realize that the wire going to the rudder tail light and happily lighting it up with DC could, and probably always is, carrying radio signal back into the system anytime the mic button is pushed. In the old days we "multiplexed" many different signals into one antenna on repeater sites with some of the radios receiving microwatts of signal from far away while other radios were pumping hundreds of watts into the same antenna at the same time. We could have powered a tower light with 60 cycle 110vac over the same wire had we wanted to. The goal of interference, noise or EMP grounding is to keep the wire doing only what you want it to do and not introduce "other" effects.
"IF" I put any electrical in my plane the ground will be wired like Steve said to a tab on the frame as close to the battery as possible using a star washer between the tab and the wire. But it's really a crap shoot with the necessary lightweight construction and mobile requirements of having to use stranded wire due to vibration. "Real ground wires" are not wires at all. At RF frequencies the signal only travels on a very thin part of the surface so anything inside is just wasted weight and copper. The best ground wire is a solid foil or solid strap. Stranded wire confuses (barnyard explanation) the signal and appears to be a higher resistance than a solid. The idea with noise is to give it the lowest resistance (R+Z) path to the negative. Panel "grounds" consisting of any Black wires coming from avionics would be attached to the panel with as short a lead as possible. The panel would be bonded to the frame as close as possible. Given the option, and if it could be guaranteed, I would insulate the panel and run one ground to the frame as close to the panel as possible. Not to a ground buss (how would I deal with the antenna coax going to ground on the wing?). I would avoid sharp bends in the wires. "Neat" looking wire is a bit like a person that has a good tan. Lot's of folks see a "model". I see skin cancer. The same with wiring. Some people see a prize winning panel at Oshkosh,with all the neatly dressed wiring and smart looking 90* bends but I see noise and spikes backing up behind those sharp bends. All right, noise be damned I would probably lay out my panel the neat way also. I would troubleshoot any noise issues after the fact. One of my favorite radios is the ARC-5 WWII bomber and fighter series Radios. Look up a inside view of one of those. The layout and wiring is simply beautiful and maybe fine for up to 7-8 Mc (oops: Mhz).
If you look at nothing else in that link I posted above check out the chart on page 86. If radio interference is what your concerned with the aircraft frequency is above 100Mhz. Entering the chart at 100 mhz we see that number ten (I bet that's solid?) wire has 828 ohms "Z" (that's impedance) per meter, so if you run 3 meters of #10 from behind the panel to the battery you have 2500 ohms AC resistance. 22 gauge is 1K ohm/meter so 3k total. I bet that is "free air solid, not next to anything or stranded, running alongside the frame, bends and other anomalies make it worse and if the frequency is higher that also makes it worse. Now the same things apply to the frame ground except with two ground paths the numbers will be different between the two causing an unbalanced condition creating a potential difference between the two grounds if you run two grounds.
This stuff may never bother you but I've learned to at least be aware of it and that has helped me troubleshoot many interference problems, glitches and bizarre unexplainable events over time in commercial radio. Ground loops are just one aspect of all this. If when you press your mic button and some other meter on the panel goes crazy or you get a strange feedback in your headphones or your electronic ignition stops sparking, the fix might be as simple as adding 8-9 inches to the power lead. If you could measure the standing waves of voltage and current on a wire, depending on frequency applied to it or picked up by it, you will find voltage peaks every few feet at aircraft frequencies. Cutting or lengthening the wire so that the voltage peak falls somewhere other than the entrance to "the meter" could eliminate the problem.
Another thing to realize is that both AC and DC can exist on the same conductor at the same time. It would be very possible to power a wing tip light from the battery over the coax going to the radio antenna. It's important to realize that the wire going to the rudder tail light and happily lighting it up with DC could, and probably always is, carrying radio signal back into the system anytime the mic button is pushed. In the old days we "multiplexed" many different signals into one antenna on repeater sites with some of the radios receiving microwatts of signal from far away while other radios were pumping hundreds of watts into the same antenna at the same time. We could have powered a tower light with 60 cycle 110vac over the same wire had we wanted to. The goal of interference, noise or EMP grounding is to keep the wire doing only what you want it to do and not introduce "other" effects.
"IF" I put any electrical in my plane the ground will be wired like Steve said to a tab on the frame as close to the battery as possible using a star washer between the tab and the wire. But it's really a crap shoot with the necessary lightweight construction and mobile requirements of having to use stranded wire due to vibration. "Real ground wires" are not wires at all. At RF frequencies the signal only travels on a very thin part of the surface so anything inside is just wasted weight and copper. The best ground wire is a solid foil or solid strap. Stranded wire confuses (barnyard explanation) the signal and appears to be a higher resistance than a solid. The idea with noise is to give it the lowest resistance (R+Z) path to the negative. Panel "grounds" consisting of any Black wires coming from avionics would be attached to the panel with as short a lead as possible. The panel would be bonded to the frame as close as possible. Given the option, and if it could be guaranteed, I would insulate the panel and run one ground to the frame as close to the panel as possible. Not to a ground buss (how would I deal with the antenna coax going to ground on the wing?). I would avoid sharp bends in the wires. "Neat" looking wire is a bit like a person that has a good tan. Lot's of folks see a "model". I see skin cancer. The same with wiring. Some people see a prize winning panel at Oshkosh,with all the neatly dressed wiring and smart looking 90* bends but I see noise and spikes backing up behind those sharp bends. All right, noise be damned I would probably lay out my panel the neat way also. I would troubleshoot any noise issues after the fact. One of my favorite radios is the ARC-5 WWII bomber and fighter series Radios. Look up a inside view of one of those. The layout and wiring is simply beautiful and maybe fine for up to 7-8 Mc (oops: Mhz).
If you look at nothing else in that link I posted above check out the chart on page 86. If radio interference is what your concerned with the aircraft frequency is above 100Mhz. Entering the chart at 100 mhz we see that number ten (I bet that's solid?) wire has 828 ohms "Z" (that's impedance) per meter, so if you run 3 meters of #10 from behind the panel to the battery you have 2500 ohms AC resistance. 22 gauge is 1K ohm/meter so 3k total. I bet that is "free air solid, not next to anything or stranded, running alongside the frame, bends and other anomalies make it worse and if the frequency is higher that also makes it worse. Now the same things apply to the frame ground except with two ground paths the numbers will be different between the two causing an unbalanced condition creating a potential difference between the two grounds if you run two grounds.
This stuff may never bother you but I've learned to at least be aware of it and that has helped me troubleshoot many interference problems, glitches and bizarre unexplainable events over time in commercial radio. Ground loops are just one aspect of all this. If when you press your mic button and some other meter on the panel goes crazy or you get a strange feedback in your headphones or your electronic ignition stops sparking, the fix might be as simple as adding 8-9 inches to the power lead. If you could measure the standing waves of voltage and current on a wire, depending on frequency applied to it or picked up by it, you will find voltage peaks every few feet at aircraft frequencies. Cutting or lengthening the wire so that the voltage peak falls somewhere other than the entrance to "the meter" could eliminate the problem.
Steve Pierce
BENEFACTOR
Graham, TX
I am in the process of wiring a Super Cub and I ran a separate ground wire from the strobe power supply on the old battery box mount to the battery under the seat. I also use the insulation washers on the headset jacks like Sigtronics shows in the wiring diagrams. Everything else has short grounds to the airframe.
Rotto
no problem it turned out to be a informative post
as for my research a friend of mine is an electrical engineer and this is his suggestion
Phil,
The final answer is in.
Connect as follows:
Battery negative terminal via hefty cable to the single point ground on the firewall.
From that point, to the engine crankcase near the starter motor with welding cable.
Connect a 10AWG wire between a nearby lug on the frame to the single point ground.
Radios etc should also connect to the single point ground (the B&C forest of tabs is good for this).
The single point ground should be bolted right through the firewall (brass), so there is a ground point on both sides.
The reasoning is this. Steel is a poorer conductor than copper, so you are adding additional resistance in the starter current path. This works out to one less connection in the starter current path as well, also reducing resistance. Although this resistance sounds small, it has a significant effect at starter currents.
Also, as I mentioned before, the steel frame will become magnetized.
2AWG versus 4AWG for the all the heavy cables (plus and minus) will cost you 2.2 pounds and reduce the voltage drop on the cable to the starter by only 4%.
The quality of these connections is more important than the resistance of the wire. Make them well.
Cheers,
Jeff
All good what your friend said IMHO except I would insulate the ground going through the firewall (talking noise again, not DC). I know this sounds strange but ask him to explain "skin effect". Attaching to one side of a piece of metal, The "RF", at 122.000 MHZ has to travel From where you attached it to the ground stud, on the surface of the metal clear across the surface on the cabin side, around the 180* bend at the edge of the firewall, then back across to the other side (engine side) back to your ground connection. It wont penetrate the bolt going through the firewall! Honest.
I know no one is going to do this but I'm attempting to explain how noise creeps into a system. DC electrons look like this marching dutifully through your firewall bolt/stud:
Good little citizens.Glitches, RF, spikes and other troublemakers look like this going all over the place except through your stud::evil:
:evil: :evil:
:evil:
:evil: :evil:
Those devil guys were supposed to be spread out but Steve's program truncates my spaces. Anyway they are devils going all over except where you want them to. The insulated ground channels them in the right direction so they don't spread out and wind up in your headset or radio. Someday someone is going to be troubleshooting a bad interference problem and maybe remember these posts.
